Members of the class of cell wall-less bacteria Mollicutes are among the smallest and simplest prokaryotes known to man. They possess very small genomes (500-1000 megadaltons) and limited biosynthetic capabilities and hence resort to either a commensal or parasitic lifestyle. The species Mycoplasma pneumoniae is a pathogen of the human respiratory tract and the leading cause of pneumonia among older children and young adults. As a graduate student I became fascinated by this microbe and focused my research on the mechanisms of pathogenesis. I sought through my post-doctoral training to become acquainted with the tools of the molecular biologist, anticipating applying molecular cloning to the study of pathogenesis. I am familiar with techniques for taking genes out of M. pneumoniae for study in Escherichia coli and am using this approach to study phase variation in mycoplasma adherence to host cells. However, the harvest of information to be gained from those studies would be enhanced immensely if cloned mycoplasma genes associated with virulence (specifically cytadsorption and oxyradical generation) could be mutated and returned to the mycoplasma chromosome in the same manner as is now common with many enbacterial pathogens. It is my goal to utilize this RCDA to expand my repertoire in genetic engineering in developing a transforation and cassette mutagenesis system for M. pneumoniae. This award would enable me to focus on the experiment problem and to spend the time interacting with microbial geneticists on this camp and nearby at Emory University so that I might make the most of homologous recombination strategies. This department has traditionally had a strong base in molecular approaches to microbial physiology and genetics, and the studies described would allow expansion of that base to include microbial pathogenesis.